The present invention presents a unit cell architecture for infrared imaging. The invention helps to extend dynamic range of near infrared (NIR) and short wave infrared (SWIR) image sensors by improving SNR value. This invention method can be applied not only infrared spectrum bands (SWIR, MWIR, LWIR . . . ) but also full spectrum light.
While a plurality of prior art references are pertinent in the field, U.S. Pat. No. 7,551,059 discloses two different input stages inside a single unit cell. One should be optimized for high and other should be for low light levels. One should be in the form of a lower gain wide dynamic range amplifier and the other should be high gain lower dynamic range amplifier. Separate outputs are present for each amplifier. The unit cell can be used for dual color detectors. The same disclosure is also published for an APS CMOS sensor readout (U.S. Pat. No. 7,616,231). The disclosure referenced herein is disadvantageous in that examples and architectures are only analog and no automatic selection circuit unit cell is presented.
Another reference U.S. Pat. No. 7,492,399, on the other hand, demonstrates need for two different input stages inside the unit cell to improve dynamic range and optimize SNR performance. The disclosure gives one specific circuit model that consists of CTIA (Capacitive Transimpedance Amplifier) and SFD (Source Follower per Detector) input stages for NIR/SWIR. Further, it is disadvantageous in that there is no automatic selection circuit and models are only analog circuit.
According to the present invention, automatic selection of input stage improves dynamic range because the best input stage amplifier is selected according to light level. And this operation is at unit cell level such that each pixel selects input stage meaning that greater dynamic range and flexibility is obtained. It is further important to note that a given user manually selects input stage according to needs. Manually selected input stage affects whole array. The two input stage architecture can be used for dual band or dual color detectors. In sum, this brings great flexibility to the architecture.